The present invention relates to a transmitter and a method as well as to a transmitting system for the wireless transmission of informational data and particularly to a technique for interference cancellation in OFDM communication.
One technique to minimize interference in wireless transmission, particularly in OFDM systems, is the so-called random orthogonal transform (ROT). The principles of ROT are described in the European patent application 98 104 287.2 of Sony Corporation which is only to be regarded to be prior art according to Article 54(3) EPC. The enclosure of said application is herewith incorporated by reference. In the following, the basic technique according to this application will be explained in detail with reference to FIGS. 8 to 10.
In FIG. 8, reference numerals 105A, 105B denote respectively portable telephone device. Reference numerals 106A and 106B denote base stations of a wireless transmission system. As shown in FIG. 8, the portable telephone device 105A uses a predetermined channel to be engaged in radio communication with the base station 106A in the cell 101A. At the same time, the same channel is used in the adjacent cell 101B so that the portable telephone device 105B is engaged in radio communication with the base station 106B. At that time, for example, in the portable telephone devices 105A and 105B both QPSK modulation (Quadrature Phase Shift Keying; Four Phase Transition Modulation) is used as a modulation method of the sent data. The signal series of the modulated sending signal are defined as x(A)2, modulated sending signal are defined as x(A)1, x(A)2, x(A)3, . . . x(A)kxe2x88x921, x(A)k, x(A)k+1, . . . and x(B)1, x(B)2, x(B)3, . . . x(B)kxe2x88x921, x(B)k, x(B)k+1, . . .
The portable telephone device 102A groups N (N is an integer which is 1 or more sending signal series x(A)n (n=1, 2, 3, . . . ). The grouped sending signal series x(A)k, . . . x(A)k+N and a predetermined Nth normal orthogonal matrix MA are multiplied in order as shown in the following equation.                                           [                          Equation              ⁢                              xe2x80x83                            ⁢              1                        ]                    ⁢                      xe2x80x83                    ⁢                      
                    [                                                                      y                  k                                      (                    A                    )                                                                                                      ⋮                                                                                      y                                      k                    +                    N                                                        (                    A                    )                                                                                ]                =                              M            A                    ⁡                      [                                                                                X                    k                                          (                      A                      )                                                                                                                    ⋮                                                                                                  X                                          k                      +                      N                                                              (                      A                      )                                                                                            ]                                              (        1        )            
As a consequence, an orthogonal conversation is added to the sending signal series x(A)n (n=1, 2, 3, . . . ) and a resulting sending signal series y(A)n (n=1, 2, 3, . . . ) are sent in order.
On the other hand, at the base station 106A which is a receiving side, when a sending signal CA is received from the portable telephone device 105A of the communication partner, N received signal series y(A)n (n=1, 2, 3, . . . ) are grouped, and the grouped received signal series y(A)k, . . . y(A)k+N are successively multiplied with an inverse matrix MAxe2x88x921 of the Nth normal orthogonal matrix MA used on the sending side as shown in the following equation.                               [                      Equation            ⁢                          xe2x80x83                        ⁢            2                    ]                ⁢                  xe2x80x83                ⁢                  
                ⁢                                                                              [                                                                                                              X                          k                                                      (                            A                            )                                                                                                                                                              ⋮                                                                                                                                      X                                                      k                            +                            N                                                                                (                            A                            )                                                                                                                                ]                                =                                                      M                    A                                          -                      1                                                        ⁡                                      [                                                                                                                        y                            k                                                          (                              A                              )                                                                                                                                                                            ⋮                                                                                                                                                  y                                                          k                              +                              N                                                                                      (                              A                              )                                                                                                                                            ]                                                                                                                          =                                                                            M                      A                                              -                        1                                                              ⁢                                                                  M                        A                                            ⁡                                              [                                                                                                                                            x                                k                                                                  (                                  A                                  )                                                                                                                                                                                                        ⋮                                                                                                                                                                          x                                                                  k                                  +                                  N                                                                                                  (                                  A                                  )                                                                                                                                                                    ]                                                                              =                                      [                                                                                                                        x                            k                                                          (                              A                              )                                                                                                                                                                            ⋮                                                                                                                                                  x                                                          k                              +                              N                                                                                      (                              A                              )                                                                                                                                            ]                                                                                                          (        2        )            
As a consequence, the signal series X(A)n (n=1, 2, 3, . . . ) is restored which is equal to the signal series x(A)n (n=1, 2, 3, . . . ) before orthogonal conversion.
In the similar manner, at the time of sending data, the portable telephone device 105B groups the N sending signal series x(B)n (n=1, 2, 3, . . . ). The grouped sending signal series x(B)k, . . . X(B)k+N and the predetermined Nth normal orthogonal matrix MB are multiplied in order for each group as shown in the following equation.                                           [                          Equation              ⁢                              xe2x80x83                            ⁢              3                        ]                    ⁢                      xe2x80x83                    ⁢                      
                    [                                                                      y                  k                                      (                    B                    )                                                                                                      ⋮                                                                                      y                                      k                    +                    N                                                        (                    B                    )                                                                                ]                =                              M            B                    ⁡                      [                                                                                x                    k                                          (                      B                      )                                                                                                                    ⋮                                                                                                  x                                          k                      +                      N                                                              (                      B                      )                                                                                            ]                                              (        3        )            
As a consequence, the orthogonal conversion is added to the sending signal series x(B)n (n=1, 2, 3, . . . ), and the resulting sending signal series y(B)n (n=1, 2, 3, . . . ) are sent in order. For reference, the Nth normal orthogonal matrix MB which is used in the portable telephone device 5B and the Nth normal orthogonal matrix MA which is used in the portable telephone device 105A are matrixes which are completely different from each other.
At the base station 106B which is a receiving side, when the sending signal CB from the portable telephone device 5B of the communication partner is received, the N received receiving signal series y(B)n (n=1, 2, 3, . . . ) are grouped, and the grounded y(B)k, . . . y(B)k+N and the inverse matrix MBxe2x88x921 of the Nth normal orthogonal matrix MB used at a sending side are multiplied in order for each group as shown in the following equation.                               [                      Equation            ⁢                          xe2x80x83                        ⁢            4                    ]                ⁢                  xe2x80x83                ⁢                  
                ⁢                                                                              [                                                                                                              X                          k                                                      (                            B                            )                                                                                                                                                              ⋮                                                                                                                                      X                                                      k                            +                            N                                                                                (                            B                            )                                                                                                                                ]                                =                                                      M                    B                                          -                      1                                                        ⁡                                      [                                                                                                                        y                            k                                                          (                              B                              )                                                                                                                                                                            ⋮                                                                                                                                                  y                                                          k                              +                              N                                                                                      (                              B                              )                                                                                                                                            ]                                                                                                                          =                                                                            M                      B                                              -                        1                                                              ⁢                                                                  M                        B                                            ⁡                                              [                                                                                                                                            x                                k                                                                  (                                  B                                  )                                                                                                                                                                                                        ⋮                                                                                                                                                                          x                                                                  k                                  +                                  N                                                                                                  (                                  B                                  )                                                                                                                                                                    ]                                                                              =                                      [                                                                                                                        x                            k                                                          (                              B                              )                                                                                                                                                                            ⋮                                                                                                                                                  x                                                          k                              +                              N                                                                                      (                              B                              )                                                                                                                                            ]                                                                                                          (        4        )            
Consequently, the signal series X(B)n (n=1, 2, 3, . . . ) which is equal to the signal series x(B)n (n=1, 2, 3, . . . ) which is equal to the signal series x(B)n (n=1, 2, 3, . . . ) before the orthogonal conversion is restored.
By the way, at the base station 106A, only the sending signal CA sent by the portable telephone device 105A reaches, but the sending signal CB sent by the portable telephone device 105B also reaches depending on the situation. In that case, the sending signal CB from the portable telephone device 105B acts as an interference wave I. When the signal level of the sending signal CB is large as compared with the sending signal CA from the portable telephone device 105A, trouble is caused to communication with the portable telephone device 105A. In other words, as the base station 106A, it is not recognized that the signal is a sending signal from either of the portable telephone devices 105A or 105B so that it is feared that the sending signal CB form the portable telephone device 105B is received by mistake.
In such a case, the base station 6A groups the N received signal series y(B)n (n=1, 2, 3, . . . ) received from the portable telephone device 5B so that the demodulation processing is performed by multiplying the inverse matrix MAxe2x88x921 to the grouped signal series y(B)k, . . . y(B)k+N as shown in the following equation as in the normal receiving processing.                     [                              Equation            ⁢                          xe2x80x83                        ⁢                          5              ⁢                              xe2x80x83                            ⁢                              
                            [                                                                                          X                      k                                              (                        A                        )                                                                                                                                  ⋮                                                                                                              X                                              k                        +                        N                                                                    (                        A                        )                                                                                                        ]                                =                                                    M                A                                  -                  1                                            ⁡                              [                                                                                                    y                        k                                                  (                          B                          )                                                                                                                                                ⋮                                                                                                                          y                                                  k                          +                          N                                                                          (                          B                          )                                                                                                                    ]                                      =                                          M                A                                  -                  1                                            ⁢                                                M                  B                                ⁡                                  [                                                                                                              X                          k                                                      (                            B                            )                                                                                                                                                              ⋮                                                                                                                                      X                                                      k                            +                            N                                                                                (                            B                            )                                                                                                                                ]                                                                                        (        5        )            
However, as seen from the equation (5), the receiving signal series y(B)n (n=1, 2, 3, . . . ) from the portable telephone device 5B is a result obtained from a multiplication of the orthogonal matrix MB which is different from the orthogonal matrix MA so that the diagonal reverse conversion is not obtained even when the inverse matrix MAxe2x88x921 is multiplied with the result that the original signal series x(B)n (n=1, 2, 3, . . . ) is not restored. In this case, the received signal series becomes a signal series which is the original signal series x(B)n (n=1, 2, 3, . . . ) orthogonally converted with another orthogonal matrix consisting of MAxe2x88x921MB, so that the signal becomes ostensibly a noise signal, and even when the signal series is QPSK demodulated, the sending data of the portable telephone device 5B is not restored.
In this manner, in the case of the radio communication system to which the present invention is applied, the orthogonal matrix which is different for each communication at the sending side is multiplied with the signal series. On the receiving side, the received signal series is multiplied with the inverse matrix of the orthogonal matrix which is used on the sending side (namely, the communication partner of its own station) so that the original signal series before the orthogonal conversion is restored. As a consequence, even when the same channel is used in the other communication, the restoration of the sent signal series by the other communication is avoided in advance with the result that the leakage of the data sent in the other communication can be avoided in advance.
For reference, there is described here that the leakage problem is avoided when the sending signal CB of the portable telephone device 105B is received by the base station 106A. For the same reason, the leakage problem can be also avoided even when the base station 106B receives the sending signal CA of the portable telephone device 105A.
Here, the orthogonal conversion using the orthogonal matrix and the inverse conversion thereof will be explained by using the signal transition view. In the beginning, the sending signal series x(A)n (n=1, 2, 3, . . . ) of the portable telephone device 105A is QPSK modulated so that the, xcfx80/4, 3xcfx80/4, 5xcfx80/4 or 7xcfx80/4 phase states can be assumed. As a consequence as shown in FIG. 9A, on the complex surface (IQ surface), the phase state is present at a position where the phase state becomes xcfx80/4, 3xcfx80/4, 5xcfx80/4 or 7xcfx80/4. When such sending signal series x(A)n (n=1, 2, 3, . . . ) is multiplied to the Nth normal orthogonal matrix MA, the resulting signal series y(A)n (n=1, 2, 3, . . . ) becomes a random state as shown in FIG. 9B.
On the other hand, at the base station 105A which is a receiving side, this signal series y(A)n (n=1, 2, 3, . . . ) is received. As described above, when the inverse matrix MAxe2x88x921 the orthogonal matrix MA which is used on the sending side is multiplied with this signal series y(A)n (n=1, 2, 3, . . . ), the resulting signal series X(A)n (n=1, 2, 3, . . . ) becomes the same as the original signal series x(A)n (n=1, 2, 3, . . . ) as shown in FIG. 9C so that the resulting signal series is brought back to the position of the phase state comprising xcfx80/4, 3xcfx80/4, 5xcfx80/4 or 7xcfx80/4 on the complex surface. Consequently, when the signal series X(A)n (n=1, 2, 3, . . . ) is subjected to QPSK demodulation, the sending data from the portable telephone device 105A can be accurately restored.
Furthermore, since the sending signal series x(B) (n=1, 2, 3, . . . ) of the portable telephone device 105B is also QPSK modulated, xcfx80/4, 3xcfx80/4, 5xcfx80/4 or 7xcfx80/4 phase state is assumed with the result that the phase is present on the position comprising xcfx80/4, 3xcfx80/4, 5xcfx80/4 or 7xcfx80/4 on the complex surface as shown in FIG. 10A. When such sending signal series x(B)n (n=1, 2, 3, . . . ) is such that the phase state becomes random as shown in FIG. 10B.
In the case where such signal series y(B)n (n=1, 2, 3, . . . ) is received with the base station 106A which is not the communication partner, the signal series y(B)n (n=1, 2, 3, . . . ) becomes an interference wave for the base station 106A. However, the base station 106A does not recognize that the signal series is either the sending signal from the communication partner or the interference wave, the demodulation processing is performed as in the normal receiving processing. However, even when the inverse matrix MAxe2x88x921 of the orthogonal matrix MA is multiplied with this signal series y(B)n (n=1, 2, 3, . . . ), the inverse matrix MAxe2x88x921 is not the inverse matrix of the orthogonal matrix MB which is used at the sending time. As shown in FIG. 10C, the phase state is not brought back to the original state so that the phase state becomes a random state. Consequently, even when the signal series shown in FIG. 10C is QPSK demodulated, the sending data from the portable telephone device 105B is not restored.
Though the randomizing according to ROT provides for an minimization of interference effects by the randomizing procedure, the interference is not canceled totally as this the case e.g. in TDMA. Furthermore, as in OFDM systems usually no training sequence or midamble is used, the distinction between a wanted and an unwanted signal generally is difficult.
Therefore it is the object of the present invention to provide for a technique which allows a more efficient interference cancellation in OFDM systems.
According to the present invention a transmitter for the wireless transmission of information data is provided. The transmitter comprises means for random orthogonal transforming (ROT) of blocks of data to be transmitted, by a multiplication of a vector comprising the data of one block with a matrix. Furthermore means for the transmission of data originating from the means for random orthogonal transforming are provided. The matrix operation uses a matrix comprising n orthogonal columns, n being the number of data samples comprised in one of said blocks. According to the present invention the number of rows of said matrix is larger than the number of said columns of said matrix. Note: Generally, when the input data are represented as a row vector, the ROT matrix has more columns than rows, and when the input data are represented as a column vector, the ROT matrix has more rows than columns. Therefore, according to the present invention an oblong matrix is provided (in contrast to the square matrix according to the prior art).
The number of rows of said matrix can be equal to M*n, n being the number of columns of said matrix and M being an integer larger than 1.
A modulator can be provided outputting said blocks of data being supplied to said means for random orthogonal transforming.
The means for random orthogonal transforming can supply the transformed data to an inverse fast Fourier transform (IFFT) circuit.
As another aspect of the present invention, the transmitter is a transmitter of the OFDM type. The means for random orthogonal transforming of blocks of data to be transmitted are provided with a plurality of mutually orthogonal matrices to provide for a frequency band division according to the OFDM system. Therefore according to this aspect, a multiple access technique for OFDM systems is provided still efficiently minimizing interference effects.
The transmitter can comprise a convolution encoder, wherein the convolution encoder is implemented by reconstructing the matrix from a convolution code matrix.
In this case the elements of the matrix are coefficients of polynomials of a convolutional function of the convolution encoder.
The coefficients of the polynomials can be shift in each column vector of the matrix implementing the convolution encoder.
The transmitter can furthermore comprise means for inverse random orthogonal transforming of blocks of data received by multiplying a received data block by a transpose matrix of the matrix used for the data to be transmitted.
Alternatively to the transpose matrix multiplication the transmitter can comprise means for inverse random orthogonal transforming an convolutional decoding blocks of data received by applying a Trellis decoding technique.
Said means for inverse random orthogonal transforming an convolutional decoding of blocks of data received can comprise means for calculating an equivalent vector of a received symbol, means for generating a Trellis state matrix on the basis of the elements of the equivalent vector, means for calculating path matrix and adding up the calculated path matrix with original state matrix, and means for deciding the decoded symbol by comparing the path matrix of the two paths leading respectively to a new state.
According to the present invention furthermore a transmitting system is provided comprising a plurality of base stations and a plurality of mobile stations. Thereby each mobile station and base station, respectively, comprises a transmitter with the features as set forth above.
According to the present invention furthermore a method for the wireless transmission of information data is provided. Blocks of data to be transmitted are processed by a random orthogonal transformation by means of a multiplication of a vector comprising the data of one block with the matrix. The data originating from the step of random orthogonal transforming are then transmitted. Thereby the matrix operation uses a matrix comprising n orthogonal columns, n being the number of data samples comprised in one of set blocks, wherein the number of rows of said matrix is larger than the number of said columns of said matrix.
According to the present invention furthermore a method for the generation of matrices to be used for the random orthogonal transformation of blocks of data in a wireless transmission chain is provided. Thereby a square matrix with orthogonal column vectors and orthogonal row vectors is provided. The square matrix is divided to great M matrices the number of rows of each of that matrices being equal to M*n, n being the number of columns of each of that matrices and M being an integer larger than one. Each of that M matrices is than allocated to a transmitter in a transmission chain.